A chitosan aqueous binder for lithium ion battery silicon negative electrode and a preparation method thereof

Abstract

The application belongs to the field of adhesive and particularly relates to a chitosan water-based adhesive for lithium ion battery silicon negative electrode and a preparation method thereof.The preparation raw materials of the chitosan water-based adhesive for lithium ion battery silicon negative electrode include chitosan, acrylic acid monomer, acrylic acid polyol ester, pH regulator, initiator and deionized water; and the mass ratio of the chitosan, the acrylic acid monomer and the acrylic acid polyol ester is (10-15):(5-10):(1-3). The chitosan is modified by using the acrylic acid monomer and the acrylic acid polyol ester, and the prepared water-based adhesive has excellent adhesive performance, and the peeling strength can reach more than 12 N / m, and is particularly suitable for lithium ion battery silicon negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of binders, specifically relating to a chitosan aqueous binder for silicon anodes of lithium-ion batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries (LiBs) are widely used in electric vehicles, portable electronic devices, and large-scale energy storage systems due to their high energy density. Silicon anodes are considered key materials for improving the performance of lithium-ion batteries. Compared to the widely used graphite anodes, silicon anodes have a theoretical specific capacity several times greater than graphite. Therefore, for the same weight or volume, silicon anodes can store more energy, further improving battery range. Furthermore, silicon, as an abundant element in the Earth's crust, is not only widely available but also inexpensive, effectively reducing battery production costs. Simultaneously, the low potential of silicon anodes allows the battery to release more energy during charging and discharging, further increasing the overall energy density of the battery.

[0003] However, during the lithiation process, silicon particles undergo dramatic volume expansion (up to 300%), which can lead to damage to the electrode structure, such as crack formation and active material shedding. These problems not only reduce the cycle stability and shorten the battery's lifespan but may also cause safety issues. Therefore, effectively stabilizing the volume changes of silicon anodes, maintaining the integrity of the electrode structure, and selecting suitable binders have become key research areas.

[0004] Silicon anode binders need to possess high strength and toughness to provide effective support and buffering when silicon particle volume changes, preventing damage to the electrode structure. Simultaneously, the binder must also possess good electrochemical stability to avoid side reactions during battery charging and discharging that could affect battery performance. Furthermore, good compatibility with the silicon anode material is also crucial for ensuring binder stability. In recent years, various novel binder materials have emerged, such as polymer-based binders, inorganic nanoparticle composite binders, and smart binders with self-healing functions. For example, Chinese patent CN116072878B discloses an electrode binder whose raw materials include chitosan, butyl acrylate, and methyl methacrylate. Although this binder has high bonding strength, its preparation requires the use of an aqueous acetic acid solution, and butyl acrylate and methyl methacrylate are primarily oily substances, making them difficult to stabilize in an aqueous environment.

[0005] Therefore, developing a water-based binder for silicon anodes that can work stably in an aqueous environment and has excellent bonding properties has significant research value and application prospects. Summary of the Invention

[0006] To address the aforementioned technical problems, the first aspect of this invention provides a chitosan aqueous binder for silicon anodes in lithium-ion batteries, the raw materials of which include: chitosan, acrylic monomer, acrylic polyol ester, pH adjuster, initiator, and deionized water.

[0007] As an implementable example, the mass ratio of chitosan, acrylic monomer, acrylic polyol ester, and deionized water is (10-15):(5-10):(1-3):(72-84).

[0008] As an example of implementation, the degree of deacetylation of the chitosan is greater than 85%.

[0009] Furthermore, the chitosan is industrial-grade chitosan, purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0010] Chitosan, a natural polysaccharide, possesses excellent film-forming and adhesive properties, enabling it to tightly bond with silicon anode materials to form a stable structure. This effectively reduces electrode material deformation and breakage during charging and discharging, significantly improving battery cycle stability and safety. Its inherent conductivity, when combined with electrode materials, further enhances the conductivity of the electrode materials, thereby increasing battery output power and energy density, and comprehensively optimizing battery performance. Furthermore, chitosan exhibits good water absorption and biocompatibility, which helps promote the compatibility between the electrode and electrolyte, forming a stable thin film that effectively blocks the interaction between the solution and solid materials in the electrolyte, further enhancing the cycle stability and safety of lithium batteries. However, the adhesive properties of single-component chitosan are limited, requiring further modification.

[0011] As an example of implementation, the acrylic monomers include acrylic acid and / or methacrylic acid.

[0012] As an implementable example, the acrylate polyol esters include one or more of the following: pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethacrylate, and triglyceride.

[0013] The carboxyl functional groups in acrylic monomers can undergo esterification reactions with the hydroxyl groups in chitosan molecules to form ester bonds, which primarily enhance the chemical stability of chitosan. Acrylic polyol esters (such as pentaerythritol triacrylate, pentaerythritol tetraacrylate, and triglyceride triacrylate) not only possess multiple acrylate groups, allowing them to further participate in crosslinking or polymerization, but their side chain hydroxyl groups also contribute to increasing molecular polarity. When acrylic monomers and acrylic polyol esters are used in combination, they can jointly modify chitosan through crosslinking reactions. The combined system not only introduces functional acrylate and hydroxyl groups, further enhancing the adhesiveness and mechanical properties of chitosan, but may also improve conductivity through structural optimization. Furthermore, due to the hydroxyl effect of the acrylic polyol esters, the modified chitosan adhesive exhibits better water resistance, thus enabling stable operation in aqueous environments.

[0014] As an example of implementation, the initiator is a peroxide-based initiator.

[0015] Furthermore, the peroxide initiator includes one or more of the following: ammonium persulfate, potassium persulfate, sodium persulfate, benzoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide, diisopropyl peroxide, dicyclohexyl peroxide, tert-butyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide.

[0016] Furthermore, the initiator includes one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0017] As an example of an implementable solution, the pH adjuster includes one of the following: sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, sodium bicarbonate aqueous solution, and ammonia solution.

[0018] As an example of implementation, the sodium hydroxide aqueous solution has a mass concentration of 1-3 wt%.

[0019] A second aspect of this invention provides a method for preparing a chitosan aqueous binder for silicon anodes in lithium-ion batteries, comprising:

[0020] S1. Add chitosan and acrylic monomer to deionized water and stir until the chitosan is completely dissolved. Then add acrylic polyol ester and initiator, and purge with inert gas for 30-60 min. Then heat the system to 45-55 ℃ and polymerize for 5-8 h.

[0021] S2. After the reaction is complete, the system is cooled to 20-30 ℃, and the pH is neutralized to 6.5-7.5 with a pH adjuster. Then, it is diluted with deionized water to a solid content of 3-8%, and stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

[0022] As an example of implementation, the inert gas includes nitrogen.

[0023] Beneficial effects

[0024] (i) The present invention selects chitosan as the main raw material for preparing the binder, which can ensure that the product has certain bonding properties. The three-dimensional network structure prepared by chitosan modification makes the binder have stronger adhesion, better anchoring silicon particles and improving the stability of the negative electrode structure.

[0025] (ii) In this invention, acrylic monomers and acrylic polyol esters are selected to modify chitosan. The three components can be cross-linked and polymerized to further improve the adhesive properties of the product, and the peel strength can reach more than 12 N / m.

[0026] (iii) In this invention, the mass ratio of chitosan, acrylic monomer, acrylic polyol ester and deionized water in the raw materials is further specified as (10-15):(5-10):(1-3):(72-84), which can prepare a lithium-ion battery silicon anode binder with excellent performance and the binder has the possibility of being used in an aqueous environment.

[0027] (iv) The binder provided by the present invention is an aqueous binder. The raw materials do not include organic solvents, the product system is relatively environmentally friendly, and the preparation process is relatively simple. It only requires adding the raw materials in a certain order, stirring, and reacting to obtain the product. Furthermore, the raw materials are widely available, the cost is relatively low, and the product has excellent performance, especially suitable for use in silicon anodes of lithium-ion batteries.

[0028] (v) Currently, the binders commonly used in lithium-ion battery silicon anodes are mostly prepared from SBR and CMC, but their bonding performance is generally poor. However, the present invention provides a novel chitosan aqueous binder for lithium-ion battery silicon anodes, which has superior bonding performance and represents a significant improvement over existing technologies. Attached Figure Description

[0029] Figure 1 This is a schematic diagram showing the peel strength of the chitosan aqueous binder for the silicon anode of lithium-ion batteries prepared in Example 1. Detailed Implementation

[0030] Example 1

[0031] The first aspect of this example provides a chitosan aqueous binder for silicon anodes in lithium-ion batteries, the raw materials for which are prepared by mass are: 150 g chitosan, 100 g acrylic acid, 30 g pentaerythritol tetraacrylate, 2.8 g ammonium persulfate, 2778 g sodium hydroxide aqueous solution with a mass concentration of 2 wt% and 3706 g deionized water.

[0032] The chitosan has a degree of deacetylation greater than 85%, is an industrial-grade chitosan, and was purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0033] The second aspect of this example provides a method for preparing a chitosan aqueous binder for silicon anodes in lithium-ion batteries, specifically as follows:

[0034] S1. By mass, add 150 g of chitosan and 100 g of acrylic acid to 720 g of deionized water and stir until the chitosan is completely dissolved. Then add 30 g of pentaerythritol tetraacrylate and 2.8 g of ammonium persulfate. Purge with nitrogen gas at 0.1 MPa for 30 min. Then heat the system to 45 °C and polymerize for 5 h.

[0035] S2. After the reaction is complete, the system is cooled to 25 °C and neutralized to pH 7.0 with 2778 g of 2 wt% sodium hydroxide aqueous solution. Then, 2986 g of deionized water is added and diluted to a solid content of 5 wt%. The mixture is stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

[0036] The peel strength diagram of the chitosan aqueous binder used for the lithium-ion battery silicon anode prepared in this example is shown below. Figure 1 As shown; a total of 2 tests were conducted, and the average of the 2 tests was taken as the final result.

[0037] Example 2

[0038] The first aspect of this example provides a chitosan aqueous binder for silicon anodes in lithium-ion batteries, the raw materials for which are prepared by mass are: 100 g chitosan, 70 g acrylic acid, 20 g glyceryl triacrylate, 1.9 g ammonium persulfate, 2778 g sodium hydroxide aqueous solution with a mass concentration of 2 wt% and 3646 g deionized water.

[0039] The chitosan has a degree of deacetylation greater than 85%, is an industrial-grade chitosan, and was purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0040] The second aspect of this example provides a method for preparing a chitosan aqueous binder for silicon anodes in lithium-ion batteries, specifically as follows:

[0041] S1. By mass, add 100 g of chitosan and 70 g of acrylic acid to 810 g of deionized water and stir until the chitosan is completely dissolved. Then add 20 g of triacrylate and 1.9 g of ammonium persulfate, and purge with nitrogen gas at 0.1 MPa for 30 min. Then heat the system to 50 °C and polymerize for 5 h.

[0042] S2. After the reaction is complete, the system is cooled to 25 °C and neutralized to pH 7.0 with 2778 g of 2 wt% sodium hydroxide aqueous solution. Then, 2836 g of deionized water is added and diluted to a solid content of 5 wt%. The mixture is stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

[0043] Example 3

[0044] The first aspect of this example provides a chitosan aqueous binder for silicon anodes in lithium-ion batteries, the raw materials for which are prepared by mass are: 120 g chitosan, 60 g acrylic acid, 10 g pentaerythritol triacrylate, 1.9 g ammonium persulfate, 1660 g sodium hydroxide aqueous solution with a mass concentration of 2 wt% and 2694 g deionized water.

[0045] The chitosan has a degree of deacetylation greater than 85%, is an industrial-grade chitosan, and was purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0046] The second aspect of this example provides a method for preparing a chitosan aqueous binder for silicon anodes in lithium-ion batteries, specifically as follows:

[0047] S1. By mass, add 120 g of chitosan and 60 g of acrylic acid to 810 g of deionized water and stir until the chitosan is completely dissolved. Then add 10 g of pentaerythritol triacrylate and 1.9 g of ammonium persulfate. Purge with nitrogen gas at 0.1 MPa for 30 min. Then heat the system to 55 °C and polymerize for 6 h.

[0048] S2. After the reaction is complete, the system is cooled to 25 °C and neutralized to pH 7.0 with 1660 g of 2 wt% sodium hydroxide aqueous solution. Then, 1884 g of deionized water is added and diluted to a solid content of 5 wt%. The mixture is stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

[0049] Example 4

[0050] The first aspect of this example provides a chitosan aqueous binder for silicon anodes in lithium-ion batteries, the raw materials for which are prepared by mass are: 150 g chitosan, 50 g methacrylic acid, 10 g pentaerythritol tetraacrylate, 2.1 g ammonium persulfate, 775 g sodium hydroxide aqueous solution with a mass concentration of 3 wt%, and 3820 g deionized water.

[0051] The chitosan has a degree of deacetylation greater than 85%, is an industrial-grade chitosan, and was purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0052] The second aspect of this example provides a method for preparing a chitosan aqueous binder for silicon anodes in lithium-ion batteries, specifically as follows:

[0053] S1. By mass, add 150 g of chitosan and 50 g of methacrylic acid to 790 g of deionized water and stir until the chitosan is completely dissolved. Then add 10 g of pentaerythritol tetraacrylate and 2.1 g of ammonium persulfate. Purge with nitrogen gas at 0.1 MPa for 30 min. Then heat the system to 45 °C and polymerize for 7 h.

[0054] S2. After the reaction is complete, the system is cooled to 25 °C and neutralized to pH 7.2 with 775 g of 3 wt% sodium hydroxide aqueous solution. Then, 3030 g of deionized water is added and diluted to a solid content of 5 wt%. The mixture is stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

[0055] Example 5

[0056] The first aspect of this example provides a chitosan aqueous binder for silicon anodes in lithium-ion batteries, the raw materials for which are prepared by mass are: 100 g chitosan, 50 g methacrylic acid, 15 g pentaerythritol tetraacrylate, 1.65 g ammonium persulfate, 465 g sodium hydroxide aqueous solution with a mass concentration of 5 wt%, and 3166 g deionized water.

[0057] The chitosan has a degree of deacetylation greater than 85%, is an industrial-grade chitosan, and was purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0058] The second aspect of this example provides a method for preparing a chitosan aqueous binder for silicon anodes in lithium-ion batteries, specifically as follows:

[0059] S1. By mass, add 100 g of chitosan and 50 g of methacrylic acid to 835 g of deionized water and stir until the chitosan is completely dissolved. Then add 15 g of pentaerythritol tetraacrylate and 1.65 g of ammonium persulfate. Purge with nitrogen gas at 0.1 MPa for 30 min. Then heat the system to 55 °C and polymerize for 8 h.

[0060] S2. After the reaction is complete, the system is cooled to 25 °C and neutralized to pH 7.4 with 465 g of 5 wt% sodium hydroxide aqueous solution. Then, 2331 g of deionized water is added and diluted to a solid content of 5 wt%. The mixture is stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

[0061] Comparative Example 1

[0062] This example provides an aqueous adhesive, which, by weight, is prepared from the following raw materials: 28 g of SBR (i.e., styrene-butadiene rubber with a solid content of 50 wt%), 6 g of CMC (sodium carboxymethyl cellulose), and 420 g of deionized water.

[0063] The water-based adhesive is prepared by mixing and stirring 28 g of SBR, 6 g of CMC and 420 g of deionized water at room temperature (25 °C).

[0064] Both the SBR and CMC were purchased from Guangzhou Songbai Chemical Co., Ltd.

[0065] Comparative Example 2

[0066] The specific implementation method in this example is the same as in Example 1, except that the raw materials used in this example do not include pentaerythritol tetraacrylate.

[0067] Performance testing

[0068] 1. Peel strength test

[0069] 300 g of the binder prepared in Examples 1-5 and Comparative Example 2 was diluted with 150 g of water, and 5 g of conductive agent and 480 g of silicon carbide material were added. After complete impregnation, the mixture was dispersed at high speed for 4 h (rotation speed: linear speed 10 m / min). 65 g of deionized water was added to adjust the viscosity. The prepared slurry was coated onto copper foil using a single-sided intermittent coating machine and baked, followed by coating (single-sided coating, areal density of 0.95 g / dm). 2 The coated electrode sheets were placed in an oven at 120 ℃ and dried for 12 h. The dried electrode sheets were then rolled, cut, and tested according to the 180° peel strength test method for adhesives in GB / T 2790-1995.

[0070] Regarding the specific test method for Comparative Example 1: 5 g of conductive agent and 475 g of silicon carbide material were added to 482 g of the binder for Comparative Example 1. After the raw materials were completely impregnated, the mixture was dispersed at high speed for 4 hours (rotation speed: linear speed 10 m / min). Then, 76 g of deionized water was added to adjust the viscosity. The prepared slurry was coated onto copper foil using a single-sided intermittent coating machine and baked, followed by coating (single-sided coating, areal density of 0.95 g / dm). 2 The coated electrode sheets were placed in an oven at 120 ℃ and dried for 12 h. The dried electrode sheets were then rolled, cut, and tested according to the 180° peel strength test method for adhesives in GB / T 2790-1995.

[0071] The conductive agent mentioned above is of the Super P type and was purchased from Shanghai Huiping New Energy Co., Ltd.; the silicon-carbon material is of the BSHC-300 type and was purchased from BTR New Materials Group Co., Ltd.

[0072] For detailed test results, please see Figure 1 See Table 1.

[0073] Table 1

[0074]

[0075] In Example 1, the peel strength is the average of two tests, and the specific peel strength test results are shown in Table 2.

[0076] Table 2

[0077]

[0078] Where, serial number 1 represents Figure 1 The data is represented by the red lines in the image.

[0079] Serial number 2 represents Figure 1 The green lines in the data.

[0080] As can be seen from the test results of Examples 1-5 above, the peel strength of the water-based adhesive prepared by the present invention is above 12 N / m, while the peel strength of the water-based adhesive prepared by SBR and CMC in the prior art is significantly lower than that of the product provided by the present invention; in addition, as can be seen from Comparative Example 2, the absence of acrylic polyol ester has a significant negative impact on the bonding performance of the water-based adhesive.

Claims

1. A chitosan aqueous binder for silicon anodes in lithium-ion batteries, characterized in that, The raw materials for preparation include: chitosan, acrylic acid monomer, acrylic acid polyol ester, pH adjuster, initiator and deionized water; The mass ratio of chitosan, acrylic acid monomer, acrylic acid polyol ester, and deionized water is (10-15):(5-10):(1-3):(72-84). The acrylate polyol esters include one or more of the following: pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethacrylate, and triglycerides. The acrylic monomers include: acrylic acid and / or methacrylic acid; The initiator is a peroxide-based initiator; The method for preparing the chitosan aqueous binder for the silicon anode of the lithium-ion battery is characterized by comprising the following steps: S1. Add chitosan and acrylic monomer to deionized water and stir until the chitosan is completely dissolved. Then add acrylic polyol ester and initiator, and purge with inert gas for 30-60 min. Then heat the system to 45-55 ℃ to carry out the polymerization reaction. S2. After the reaction is complete, the system is cooled to 20-30 ℃, and the pH is neutralized to 6.5-7.5 with a pH adjuster. Then, it is diluted with deionized water to a solid content of 3-8%, and stirred evenly to obtain a chitosan aqueous binder for silicon anodes of lithium-ion batteries.

2. The chitosan aqueous binder for lithium-ion battery silicon anodes according to claim 1, characterized in that, The degree of deacetylation of the chitosan is greater than 85%.

3. The chitosan aqueous binder for lithium-ion battery silicon anodes according to claim 1, characterized in that, The peroxide initiators include one or more of the following: ammonium persulfate, potassium persulfate, sodium persulfate, benzoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide, diisopropyl peroxide, dicyclohexyl peroxide, tert-butyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide.

4. The chitosan aqueous binder for lithium-ion battery silicon anodes according to claim 1, characterized in that, The pH adjuster includes one of the following: sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, sodium bicarbonate aqueous solution, and ammonia solution.

5. The chitosan aqueous binder for lithium-ion battery silicon anodes according to claim 4, characterized in that, The sodium hydroxide aqueous solution has a mass concentration of 1-3 wt%.

6. The chitosan aqueous binder for lithium-ion battery silicon anodes according to claim 1, characterized in that, The inert gas mentioned includes nitrogen.

7. The chitosan aqueous binder for lithium-ion battery silicon anodes according to claim 1, characterized in that, The polymerization reaction in step S1 takes 5-8 hours.

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